Various monitors are known for measuring biological or physiological characteristics of a patient. Most of these monitors include some type of sensor for sensing a biological signal representative of the characteristic. The sensor usually includes a transducer and often is coupled by a flexible cable to a processor and a display unit for displaying information about the monitored biological signal. One important class of such monitors is ultrasound fetal monitors commonly used for detecting and displaying the heart rate and other physiological characteristics of a fetus in vivo. In operation, the hand held sensor containing the transducer of such a monitor is typically positioned on the abdomen of the mother by a skilled operator, such as a physician or attending nurse. The accuracy of such monitors degrades quickly as the transducer is moved away from an optimal location on the abdomen, so it is important that the transducer be positioned accurately. The fetus is often active and frequently moves within the womb making optimum placement of the transducer sometimes difficult and time consuming, when the exact position of the fetus is unknown. When activated, the transducer generates ultrasound signals that penetrate the body of the mother. The transducer also receives ultrasound echoes that are reflected by the fetus, as well as by internal structures of the mother's body, and generates electrical signals representative of the received ultrasound signals. While the range and direction of the transmitted ultrasound can be controlled between certain limits, they are usually quite limited so that if the sensor is incorrectly positioned relative to the fetus, no echoes from the fetus will be sensed. If correctly positioned, the transducer will convert the ultrasound echo signals representative of the heart beat of the fetus into an electrical signal which is transmitted over the flexible cable to the processor. The processor analyzes these electrical signals to determine the heart rate and other physiological characteristics of the fetus. The output of the monitor, including an indication of the fetal heart rate, is visually displayed by the display unit which may be implemented as a cathode ray tube type display or a light emitting diode (LED) type display, or the like. The display unit is typically positioned remotely from the transducer on a shelf or a cart.
Prior art fetal monitors suffer from the disadvantage that the operator can not conveniently view the output of the display unit while positioning the transducer. Since the accuracy of such monitors degrades rapidly as the transducer is moved away from an optimum position, it is important that the operator watch the display unit to evaluate whether the heart beat is being sensed and whether the strength of the sensed signal is adequate. Typically, the operator places the transducer on the patient and then, while holding the transducer in place, turns to view the display unit. By viewing the output of the display unit, the operator can determine whether the transducer is positioned optimally. If the transducer is not optimally positioned, the operator then either continually moves the transducer while watching the display, or looks at the display between successive movements of the transducer, trying to find the optimal position of the transducer, where the signal strength of the echoes is at a maximum or near maximum, or at least sufficiently strong so that the processor can accurately process the signal information sensed by the transducer. In any case the operator takes his or her eyes off the patient, which can make the patient uncomfortable. The process of adjusting the position of the transducer is repeated until the operator determines that the transducer is positioned sufficiently well for the monitor to function accurately. Once the transducer is so positioned, the transducer is usually fixed to the mother by a strap, or tape, or the like. While being monitored, should the fetus move sufficiently away from the sensor, the process must be repeated. Such monitors are therefore awkward and inconvenient to operate, because the operator must, either take his or her eyes off the patient, or continually turn back and forth between the transducer and the display unit when positioning the transducer.